Beogram 8000 Type 5613: Reassembly to Record Play

After this Beogram 8000 turntable service manual adjustments were made and operations checked out my focus shifted to reattaching the loose deck and door panels.

Pretty much every Beogram 8000 and 8002 turntable at this point in time will experience failing foam type, double-sided tape that Bang & Olufsen used in the eighties to attach the metal deck and tonearm compartment door. The fix is to remove the old, deteriorating tape residue, clean the parts and reattach them with modern glue or tape. I prefer using modern 3M VHB type tape that the automotive industry uses. For this Beogram I am using their RP32 VHB tape. It is 0.032 inches (32 mil) thick which should be just right.

First however, I have to clean off the old tape residue. My product of choice for that task is GooGone.

I usually let it soak overnight. That gives the GooGone a good amount of time to work where it is fairly easy to scrape away the old tape. It is also very messy so have paper towels on hand.

This Beogram arrived with the old tape already removed from the tonearm compartment door panel and hinge already clean so I started there on the reassembly.

Next was the aluminum deck panel.

Now I could start putting the working turntable components back in the cabinet.

No surprises here as the turntable components had already been tested out on my bench.

This Beogram is ready for some record play.

I connected it to my Beomaster 6000 where it will live for a few days as I test it out playing records.

A nice reward.

Beogram 4004 (5526): Replacing the Light Bulbs in the RPM Trimmer Panel with LED Assemblies

The two remaining light bulbs to be replaced in the Beogram 4004 (5526) that I am restoring right now were in the RPM trimmer panel. It is a good idea to replace these bulbs with LED assemblies since they can influence the RPM stability of the platter motor due to their radiated heat that can change the resistance of the RPM trimmers in some cases.

This shows the RPM trimmer panel after taking it out:

I removed the bulb covers

and extracted the bulbs:

This shows the LED assemblies:

I installed them:

and put the covers back on:

This shows the 33 RPM scale illuminated by the LEDs:

The LED assembly combines red and green LEDs to achieve a 'natural incandescent' look, while providing red photons for properly illuminating the scale hand.

Beogram 8000 Type 5613: Service manual checks and solving an old tonearm lowering problem

This Beogram 8000 project is getting close to complete. The electrical work has been done and a sensor problem was solved in the last post. Now it is time to do the service manual checks and adjustments.

Similar to the Beogram 4004 the Beogram 8000 calls for the top surface of the platter to be 23mm from the top of the fixed arm. I made the check with my usual measuring tool.

Note that to operate all of the Beogram 8000 functions other than the turntable platter you can disconnect the P4 connector on the main board. That will leave the platter disabled during the testing.

No adjustment necessary here.

Before the next service manual adjustment I wanted to check the Beogram 8000 arm lowering function. With Beogram 8000 and 8002 turntables the damping of the arm lowering mechanism is accomplished electronically. Various owners (myself included) have experienced weird occurances of the tonearm dropping without any damping. The click of the solenoid could be heard in these cases, then after a short delay, the arm suddenly drops all the way down to the record. The first thoughts about this was there must be some defect in the electronic control for the arm lowering. Afterall, the electronic circuit is in control. While that is a possibility it is far less likely than the problem being mechanical.

The last time I ran into this problem I discovered some FOD (foreign object debris) in the lowering mechanism that was causing the problem. This turntable did not have any obstructions. I had made a point to check that earlier in the project. So I was surprised when I discovered this turntable indeed suffers from the sudden tonearm drop problem. I was kind of happy about it as maybe I could finally get to the bottom of this.

Here is evidence of the problem.

At the arm raised position you can see that the arm raise/lowering solenoid is to the right of its housing. The raise/lowering bar is in contact with the tonearm connection point (to the bar). This is all proper.

Here is the problem though.

The arm raise/lowering solenoid is now all the way to the left of the housing...in the arm lowered position. The arm raise/lowering bar has raised up to allow the tonearm to lower...but look, the tonearm connection point remains down at the arm raised position.

The way this should work is the gravity from the tonearm phono cartridge tracking force setting (typically 1 gram) should keep the connection point on the arm raise bar as it goes up.

After a short delay the arm finally does drop down suddenly. Why?

After checking the tonearm assembly pivot pins for lowering I discovered that they were operating fine and without any obstruction. I couldn't feel anything preventing the arm lowering when the lowering bar was moving to the lowered position. Very strange.

I was able to operate the arm raise/lowering bar manually and duplicate the delayed tonearm drop. Exercising that several times I increased the cartridge tracking force to 2 grams. Now the tonearm lowered correctly every time.

So the problem was that at 1 gram there was some force it had to overcome to lower.

The only mechanical suspect left was the adjustment screw that sets the height of the tonearm relative to the fixed arm. That screw physically touches the bottom of the tonearm counterweight.

My guess is the metal to metal contact develops into some sort of delayed release for the tonearm lowering. As a test solution I cut a small rectangular piece of Dura-Lar and glued it to the base of the tonearm counterweight where the adjustment screw contacts it.

That appears to have fixed the problem. Now the arm lowers gently when the electronic damping control moves the solenoid.

You can see that the tonearm connection point remains in contact with the arm lowering bar.

When the Beogram is all assembled the tonearm will contact and be playing a record before the arm raise/lower bar is at its full travel point. So in real operation the bar will have some separation from the tonearm contact point during record play.

Whew!  I think that mystery is solved now.

On to the cartridge tracking force check.  No problem there.

The last service manual adjustment/check before trying to play a record is the tangential tracking sensor.  As the cartridge stylus travels the record grooves the Beogram must sense the movement and keep tangential arm assembly moving to remain tangential to the stylus tracking path.

Like the Beogram 400x turntables the sensor is an optical sensor with an adjustment for the sensitivity of the tracking. The service manual calls for the adjustment to be made where the tracking motor first advances after two revolutions of the platter (± 1 revolution). After that the tracking motor should advance on every revolution of the platter.

Here is the adjustment point.

Here is the check of the adjustment.

Now I can hook up the P4 connector so the platter motor is enabled.  Note: Always disconnect and connect the board connectors with the Beogram unplugged.

There it is. Another Beogram 8000 turntable ready for reassembly and real record play.

Beogram 8000 Type 5613: Repaired tangential arm position sensor (0PE1)

In the last post I ended with the tangential arm position sensors failing to generate the necessary pulses for the Beogram 8000 microcomputer to tell where the tonearm is.

Since neither of the two position sensors had a signal I reasoned that the problem is likely with the sender, an infrared emitter device. So I decided to replace that device and see if it fixes the problem.

Here is the 0PE1 tangential arm position sensor assembly

After replacing the emitter device with a new OP240A infrared emitter the sensor assembly was sending signals back to the microcomputer and the tangential arm position could be determined again.

Beogram 8000 Type 5613: Testing the power supplies and sensor signals

The initial restoration tasks are all completed so it is time to assemble and see what happens when the Beogram is plugged in to the AC socket.

Pressed "Play"
That's a good sign when the turntable starts to work. The question now is what do the supply voltages and sensor signals look like?

I measured the +5VDC supply voltage at the microcomputer board across the C28 capacitor I replaced.

Then I checked the ±15VDC supply voltages.

The power supplies all measure good.
Now for the LDR scanning sensor signals. Those are the forward (<<) and reverse (>>) scanning operations. The service manual calls for around 620mVDC on those signals when they are not pressed.

Here is the related circuit.

I removed the LDR sensor assembly cover to check if the sensor lamp was on. It was.

Now I can make use of my test connector to see what the voltages look like.

These needed some adjusting.
Here are the signals after I made the necessary adjustments (turning the screws on the LDR assembly cover). I always try to set the two sensors at values close to each other and at a non-pressed value of between 620mVDC and 700mVDC.

The next sensor I checked was the platter speed sensor.
Here is the circuit

Here is the actual measurement point for my oscilloscope probe.

Here are the signals for the two platter speeds coming from the tachodisc sensor.

Now for the sensor in the fixed arm that detects the presence of a record on the platter.

Here is the actual measurement point I used.

I checked the sensor at  33⅓ RPM

The signal looks like it is supposed to. It matches up with the service manual description.

The last sensor I checked on this power test run was the tangential arm position sensor.
Here is that circuit.

There is actually one source device and two sensors for the arm position. Both sensors generate pulses when the spindle turns and the Beogram microcomputer counts them to keep track of where the tangential arm carriage is. That allows the microcomputer to know the set down points and the end point of a record.

Here is where I placed my oscilloscope probes.

Initially and through the other sensor tests the arm position detection was working correctly. I even measured the output signals of the two sensors (as they come of their OpAmps).

Then the sensor signals died.

The Beogram cannot function without the arm position known and without the sensor signal the microcomputer counter is lost.

I rechecked the supply voltages and all of the other sensors again. They are all still working. It is just this position sensor circuit that is failed.

I have spare devices for the position sensor assembly so I will dig into that next. The problem could just be a connection so I will check that out first.